1. Field of the Invention
The present invention relates to an apparatus for the regulation of a gas volume delivered to a patient during a respiratory cycle, said apparatus comprising at least one valve for discharging some of the propellant gas which flows from a propellant gas source into a propellant gas chamber, and said propellant gas chamber being at least partially defined by a wall with a second chamber on the other side thereof and the location of said wall changing as the pressure of propellant gas increases in the propellant gas chamber to increase the volume of said propellant gas chamber, whereby the volume of said second chamber on the other side of the wall diminishes, forcing the gas to be delivered to a patient to flow towards a patient whereafter, in order to perform the exhalation of patient through the valve, the pressure of said propellant gas chamber is allowed to discharge for diminishing the volume of the propellant gas chamber and increasing the volume of the second chamber as a result of the wall displacement. The invention relates also to a method for regulating a gas volume.
A ventilator is a respiratory device for carrying out the ventilation of a patient's lungs when the patient's own respiratory action is insufficient or completely stopped.
The structure of ventilators using a pressurized gas as the propelling force can be divided in three components: a control unit, a bellows unit, and a patient circuit. An object of the control unit is to carry out control parameters characterizing the pulmonary ventilation; such as tidal volume, respiration frequency, the ratio of inhalation and exhalation times as well as an inhalation pause. The bellows unit separates patient circuit unit and the patient loop of a ventilator using a pressurized gas as the propelling force. An object of the bellows unit is to prevent the respiratory gases of a patient and the propellant gas from mixing with each other. An object of the patient circuit is to provide separate passages for inhalation and exhalation gases to and from a patient as well as to remove carbon dioxide from exhalation gases.
2. Description of the Related Art
Traditionally, in ventilators using a pressurized gas as the propelling force, a tidal volume to be delivered into a patient's tube system is determined by means of a propellant gas flow and its duration. In U.S. Pat. No. 4,637,385, a propellant gas flow is regulated by throttling a gas source with a needle valve. The position of the needle valve can be controlled by means of a microprocessor and a motor. The position of the needle valve is indicated by a mechanical signal which is converted into an electric signal. Drawbacks of this solution include sensitivity to calibration errors and needle valve malfunctions.
EP Patent publication No. 282,675 describes a flow control valve intended for a ventilator, to which is delivered a stabilized propelling pressure from a gas source. A patient's respiratory gases are carried through said valve under the control of a stepping motor and a microprocessor. The flow control valve is regulated by a stepping motor with predetermined control data for delivering a tidal volume to a patient. Said valve is opened to match a required inhalation flow and it is kept open for the duration of a tidal volume delivery. A microprocessor is used to compensate for the effect that the flows occurring at the time of opening and closing the valve have on the tidal volume. The control valve operates on an open-loop principle, which is characterized by inaccurate control. The compensation of an opening and closing time requires a high peak flow. If this is to be minimized by using a high-speed valve, the accuracy of ventilation will be impaired even further.
U.S. Pat. No. 4,256,100 discloses an anaesthesia ventilator, wherein a propellant gas flow is controlled by five binary weighted valves. A regulated propellant gas pressure is delivered according to a predetermined flow through one of the valves into a collecting chamber and further to a bellows unit. The maximum temporary flow is achieved when all valves are simultaneously open. A tidal volume is determined in relation to preset respiration frequency, inhalation and exhalation times as well as by means of a flow rate per minute by using a microprocessor. A problem in the cited invention is that the realization of a large dynamic area together with resolution requires a plurality of valves. For example, a peak flow of 100 1/min. and a resolution of 0.1 1/min. require ten valves and, thus, the solution will be expensive, complicated, bulky and demands a lot of power.